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Our service used to send an an audible alert tone, like QCII over the air. IN Digital this seems impossible the XPR7550 series radios (and perhaps all XPR) filter out all audio wave forms (sine waves) except for DTMF and voice.

I'm trying to understand how this works, why it's necessary in digital and if there is a work around to get an audible tone to broadcast.

I could find anything with a search but I imagine this has been discussed, any further information would be appreciated.

Longer answer. If digital radio just sampled the data and pushed it over the air, you would need about 64kbits/sec to handle voice. That would require about 32 to 64 kHz of bandwidth to carry in any reasonable modulation for what we are doing. The point of digital is to reduce, not increase, bandwidth. So in order to make that work it is necessary to reduce the number of bits needed. This is done by using a vocoder, specifically AMBE (Advanced Multi Band Excitation). AMBE works by comparing the incoming data against a "codebook" of the sorts of sounds used in speech, and then just transmitting information about what code was the best fit. The codebook has entries for voice things, like sssss or aaaah, and for things like dial tone and DTMF. It doesn't have entries for things like QCII, so it won't find a good enough match to allow the decoder to faithfully reproduce the signal.

This is my opinion, not Aeroflex's.

I WILL NOT give you proprietary information. I make too much money to jeopardize my job.

I AM NOT the Service department: You want official info, manuals, service info, parts, calibration, etc., contact Aeroflex directly, please.

noloflashradio wrote:Motorola told me that if we would use a console to dispatch it could put out the tones...how would that work over DMR?

It doesn't really "put out the tones" - it inserts bits into the DMR protocol frames for signaling things like that, rather than trying to encode the tones in the parts of the DMR protocol frames reserved for voice data.

This is my opinion, not Aeroflex's.

I WILL NOT give you proprietary information. I make too much money to jeopardize my job.

I AM NOT the Service department: You want official info, manuals, service info, parts, calibration, etc., contact Aeroflex directly, please.

So I did a quick audio sweep from 290 hz to 3500 hz on a XPR5550 a couple days ago. Audio was injected into the accessory port of the XPR5550(transmit radio). The receiver was a XPR7550e. Everything setup for digital simplex. Surprisingly the XPR7550e did an excellent job of re-producing all tones within that frequency range, at least with a trained ear. Two-tone paging sounded excellent, no audible distortion could be detected. So from my little test it appears that you may be able to send an audible tone across TRBO radios, but as of now there isn't anything to my knowledge available to decode that tone. If you just need to hear the tone then it should work fine.

ard099 wrote:So I did a quick audio sweep from 290 hz to 3500 hz on a XPR5550 a couple days ago. Audio was injected into the accessory port of the XPR5550(transmit radio). The receiver was a XPR7550e. Everything setup for digital simplex. Surprisingly the XPR7550e did an excellent job of re-producing all tones within that frequency range, at least with a trained ear. Two-tone paging sounded excellent, no audible distortion could be detected. So from my little test it appears that you may be able to send an audible tone across TRBO radios, but as of now there isn't anything to my knowledge available to decode that tone. If you just need to hear the tone then it should work fine.

I duplicated this test using the same equipment (XPR5550 and 7550e) with the same successful results only I used the QCII audio I'm trying to get to work.Here is how I plan to use it in the the real world. We dispatch using XPR75501. the 7550 will send an alert (text) message to the XPR55502. using either sound sniffer software and a usb relay from a computer [or the pin26 relay if I can't get the computer to work right] the 5550 will be keyed up and play the sound either from a computer (it's already connected for recording anyway)

Our preliminary tests show that this will work.....It's a little crazy but now I see there is no reason that I can think of as to why Motorola didn't design the XPR7550 with tone over digital...It looks like it should be able t work.